For improving the optical appearance of surfactant compositions, for example liquid detergents and cleansing agents (i.e. floor cleansing agents, washing-up liquids or similar products) or liquid body cleansing and body care compositions as well as hair treatment compositions (i.e. shampoos, bath additives, liquid soaps, shower gels or similar products), aqueous pearlescent dispersions (pearlescent concentrates) are frequently added to these, whereby a pearlescence and thus an esthetically pleasing external appearance is imparted to the surfactant compositions.
The known aqueous pearlescent dispersions consist essentially of at least one pearlescent compound (also called a pearlescent component or pearlescer), at least one dispersant (also called a solvent, wetting agent or emulsifier) and water. Numerous pearlescent compounds and compound mixtures are recommended in the prior art, for example fatty acids, fatty acid mono- or fatty acid dialkanolamides, monoesters or diesters of alkylene glycols such as ethylene glycol, propylene glycol or oligomers thereof with fatty acids (fatty acid glycol esters) and also monoesters or polyesters of glycerol with higher fatty acids. Even more numerous are the compounds that are described as dispersants, for example alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, amine oxides, betaines, addition products of ethylene oxide and/or propylene oxide to fatty alcohols, fatty acids or alkylphenols and also glycerol mono- or glycerol diesters or sorbitan mono- or sorbitan diesters of fatty acids, in which the glycerol esters and sorbitan esters are optionally ethoxylated and/or propoxylated, alkyl mono- or alkyl oligo-glycosides and the like.
The immediate prior art is very well represented in the following patents and patent applications.
U.S. Pat. No. 7,268,107 discloses a pearlescent composition that contains from about 30 to 55% by weight of a pearlescent wax, a nonionic dispersant, optionally a zwitterionic dispersant, about 0.1% by weight to 5% by weight of a polyol ester and water, in which the active content (sum of the content of pearlescent component and dispersant) is at least about 55% by weight based on the weight of the composition and the sum of the content of dispersants is less than 25% by weight based on the weight of the composition and in which the nonionic dispersant and the polyolester are present in a weight ratio of about 5:1 to 10:1.
US patent application US 2004/0086470 A1 relates to an aqueous pearlescent composition that contains approximately 30 to 60% by weight of a wax component, which consists to at least 15% by weight, based on the weight of the wax component, of amorphous particles and to at most 85% by weight, based on the weight of the wax component, of crystalline particles, and approximately 5 to 25% by weight of a surfactant, selected from a nonionic surfactant, an amphoteric surfactant and mixtures thereof.
U.S. Pat. No. 6,727,217 B1 relates to a process for the production of pearlescent surfactant compositions at a temperature of approximately 10° C. to 45° C., in which an aqueous surfactant solution is contacted with a composition of a pearlescent wax and a polyol ester.
U.S. Pat. No. 6,835,700 B1 discloses a fluid pearlescent concentrate that comprises approximately 25 to 45% by weight of a pearlescent wax, approximately 35 to 40% by weight of a nonionic, amphoteric, zwitterionic and/or cationic dispersant, approximately 0.5 to 15% by weight of a polyol ester and water, in which the sum of the content of wax, dispersant and polyol ester is at least 55% by weight.
U.S. Pat. No. 6,147,124 A relates to fluid, bio-degradable pearlescent concentrates that contain 5 to 50% by weight of an alkanol ether or of an alkanolamide as the pearlescent component, 5 to 55% by weight of a fatty acid M-alkyl polyhydroxyalkylamide as the sole nonionic dispersant and 0.1 to 40% by weight of a low molecular weight polyol.
U.S. Pat. No. 6,235,702 B1 relates to an aqueous pearlescent concentrate that contains 1 to 99% by weight (based on the total weight) of an ester of a hydroxyl group-bearing carboxylic acid with a fatty alcohol, 0.1 to 90% by weight (based on the total weight) of a dispersant, selected from an anionic surfactant, a nonionic surfactant, a cationic surfactant, a zwitterionic surfactant, an ester quat and mixtures of these, and up to 40% by weight (based on the total weight) of a polyol.
U.S. Pat. No. 6,228,831 B1 discloses a pearlescent concentrate that contains 1 to 99.9% by weight of a fatty component, selected from the group consisting of fatty alcohols, fatty ketones, fatty ethers, fatty carbonates and mixtures of these, 1 to 99.9% by weight of a dispersant selected from the group consisting of anionic, nonionic, cationic, ampholytic and zwitter-ionic surfactants and mixtures of these, and up to 40% by weight of a polyol.
U.S. Pat. No. 5,711,899 relates to fluid pearlescent concentrates that contain 15 to 40% by weight of a pearlescent component, 5 to 55% by weight of a nonionic, ampholytic and/or zwitterionic surfactant and 0.1 to 5% by weight of a low molecular weight polyol.
U.S. Pat. No. 6,165,955 relates to a pearlescent concentrate with high temperature stability, that consists of a pearlescer based on a fatty acid selected from the group consisting of hydroxylstearates, polyethylene glycol mono- and distearates, ethylene glycol mono- and distearates, stearic acid monoethanolamide and mixtures of these, in which at least 90% by weight of the fatty acids of said fatty acid constituent consist of octadecanoic acid.
European patent application EP 0 568 848 A1 relates to fluid aqueous pearlescent dispersions that essentially consist of a fatty acid glycol ester as the pearlescence-imparting component, of two specific surfactant compounds, namely a betaine and a fatty alcohol alkoxylate, and water in a specific amount in each case.
Such pearlescent formulations additionally contain, besides the alkyl ether sulfates and/or alkyl sulfates and/or alkyl sulfonates employed in surfactant compositions as key substances, a series of auxiliaries such as, for example, amine oxides, betaines, addition products of ethylene oxide and/or propylene oxide to fatty alcohols, fatty acids or alkylphenols, glycerol mono- or glycerol diesters or sorbitan mono- or sorbitan diesters of fatty acids; in which the glycerol esters and sorbitan esters are optionally ethoxylated and/or propoxylated, alkyl mono- or alkyl oligo-glycosides, alcohols, polyols and the like.
The concentration of the key substances employed here is in general less than 35% by weight. Such lowly concentrated pearlescent formulations mainly have economic disadvantages. In direct comparison to the highly concentrated pearlescent formulations, transport, packaging and storage costs in particular matter here.
The production of pearlescent dispersions in the prior art generally takes place batchwise in stirred reactors. In this process, the necessary amounts of the substances employed are metered into a mixing vessel, heated to 5-20° C. above the melting temperature of the highest-melting component and mixed. After mixing, the mixture is first cooled to 30-40° C. with stirring without cooling. Only after reaching this temperature is it cooled to room temperature using cooling.
A check generally takes place only on the finished product of the corresponding mixing batch. Continuous checking of the production process is generally not possible.
In addition, highly concentrated pearlescent dispersions can generally not be produced by the conventional processes, as due to the high viscosity of such compositions problems in the thorough mixing of the components occur. On account of the high energy input by the stirrer necessary for thorough mixing, such processes are on the one hand very energy- and cost-intensive and on the other hand the stirred material is very strongly heated, which in turn adversely affects the quality of the product.
Moreover, a variation of the amounts of product in the prior art is only possible to a very restricted extent, since the possible batch size with a batch mixer lies in a narrowly restricted range. The minimal batch size must generally not fall below half of the maximum batch size.
The patent application WO 2004/082817 A1 discloses an apparatus and a process for the continuous production of emulsions or dispersions. The apparatus described comprises a mixing vessel closed on all sides, that has supply and outlet pipes for the entry and discharge of fluid substances or substance mixtures as well as a stirrer and that allows a stirred entry into the emulsion or dispersion without production of cavitation forces and without high-pressure homogenization.